1. Field of the Invention
The invention finds application in the dental field, in particular in the production of dentures.
2. Related Technology
The most common technique for the production of dentures is the following. The dentist takes imprints of the teeth of the upper jaw and the lower jaw of the patient. Plaster models of the upper jaw and the lower jaw are produced from the imprints. These are placed in an articulator which consists of two parts which are connected with each other by two joints and which simulate the human set of teeth. The two joints correspond to the human jaw joints. After putting the plaster models in place the joints must be adjusted patient specifically.
A known method for the determination of the centric position consists in that a plate-like plastically deformable register is inserted between the opened teeth of the patient and the patient is then caused to bite. Through this imprints of the teeth of the upper jaw and the lower jaw are formed in the register. After hardening, the register is placed between the plaster models of the upper and lower jaw emplaced in a registry. Then, the lower jaw is displaced relative to the upper jaw, by adjustment of the two joints of the articulator representing the jaw joints, for so long that the teeth of the plaster models of the upper and lower jaw engage into the imprints on the two sides of the register with fitting seating.
Another likewise known method consists in that in each case a plate is fastened, in the mouth of the patient, to the teeth of the upper jaw and the lower jaw by means of a plastically deformable mass. The two plates extend through the oral cavity. The plate fastened to the teeth of the lower jaw carries a supporting pin rising up in the middle. The plate fastened to the teeth of the upper jaw has a wax layer at its underside in which the supporting pin, upon impingement, produces an imprint. The imprint defines the centric position. The two plates are then removed from the mouth of the patient and put onto the teeth of the plaster models in the articulator. The joints of the articulator are then so displaced that the supporting pin again dips into the imprint of the wax layer at the underside of the upper plate. With that, the articulator is adjusted to the centric position. Thus, here, the centric position is a reference position fixed in the patient mouth and in employed in the articulator for adjustment.
A third known method for the determination of the centric position is a variation of the second method just described. Here, the patient is not only caused to bite once, but rather his lower jaw is to carry out a fore and back movement, as well as side movements to two sides. Thereby, a T-like trace arises in the wax layer of the upper plate, wherein the upper T-limb is upwardly arched. One calls this arching a Gothic arch. The intersection point of the two T-limbs is now selected as that point with which the support pin is lined up in the articulator for adjusting the centric position.
There is also known a device sold by Kaltenbach & Voigt GmbH (Germany) under the trade name “Digma” or “ARCUS-Digma”. This device is an aid for the setting of articulators. For this purpose, it carries out an electronic position analysis of the lower jaw. To measure the movements of the lower jaw with respect to the upper jaw in each case there is connected with the upper jaw and the lower jaw a carrier frame. The carrier frame connected to the upper jaw at the upper part of the head has four microphones; the carrier frame connected to the lower jaw has three ultrasound transmitters. The twelve paths between the three transmitters and the four microphones are evaluated with regard to their length changes upon movement of the lower jaw. Up to now, the device has not found any application for the determination of the centric position.